Piston-ring rough-grinding machine



Oct. 13, 1925 C. JOHNSON PISTON RING ROUGH GRINDING MACHINE '1 Sheets-Sheet '1 Inuen Filed Jan. 9, 1922 Gh'aNesEJohnson Oct. 13, 1925.

Filed Jam 9, 1922 '7 Sheets-Sheet 2 mm GhaflesEJohnson 5%;M;v

C. E. JOHNSON PISTON RING ROUGH GRINDING momma F le n 1922 'r Sheets-Sheet 3 InueMor Ghaflesfldohnion Oct. 13, 1925- c. E. JOHNSON PISTON runs aouenhnmnms momma Filed Jan. 9, 1922 '7 Sheets$haet 4 Invenfor GharlesEJohnson Oct. 13,1925- 1. 6395 C. E. JOHNSON PISTON RING ROUGH GRINDING MACHINE Filed Jan. 9, 1922 '7 Sheets-Sheet 5 Inbenfor Charles Edohnson 3 $7M (-lfiforneg Oct. 13, 1925- 1,556,995 c. E. JOHNSON v PISTON RING ROUGH GRINDING "ROBIN! F le n- 1922 "'1 Shouts-Shoot e lnuenijor Churlesldohnson C. E. JOHNSON PISTON RING ROUGH GRINDING MACHINE Filed Jan. 9, 1922 7 Sheets-Sheet 7 InvenTQr, Charles DJohns,

Patented Get. 13, 1925.

UNITED STATES CHARLES E. JOHNSON, OF MUSKEGON, MICHIGAN.

PISTON-RING ROUGH-GRINDING MACHINE.

Application filed January 9, 1922.

To all whom it may concern.

Be it known that 1, CHARLES E. JonNsoN, a citizen of the United. States of America,

residing at Muskegon, in the county of Muskegon and State of Michigan, have invented certain new and useful Improvements in Piston-Bing Rough-Grinding Machines; and I. do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to a machine for finishing the ends of individual piston ring castings to a rough ground finish. In the manufacture of piston rings, one method followed is to cast individual ring castings which, after coming from the moulds have to be finished to proper size on the ends and outer curved surfaces thereof. To do this requires several operations and it is to the accomplishment of one of the finishing operations that the machine of my invention is directed, The ring castings are first rough ground at their ends. My invention has for its primary object and purpose the provision of a machine with which piston ring individual castings may be rough ground at both ends with great rapidity and with accuracy, whereby quantity production of the. piston rings is facilitated. Subsidiary to the primary object and purpose of the invention are many others, concerned chiefly with the production of a machine of the character outlined which is durable and in no way liable to get out of order so that.

it can be kept continuously running, and one which requires little attention and can be supplied with the rough ring castings by unskilled labor,the labor cost. connected with the. operation of the machine being reduced to a minimum. All of these features, as well as many others not specifically enumerated at this time, will appear fully andin detail as understanding of the invention is had from the following description, taken in connection with the accompanying drawings, in which,

Fig. 1 is a side elevation of the grinding machine of my invention.

Fig. 2 is a plan view thereof.

Fig. 3 is a vertical transverse section taken substantially on the planes of the broken line 33, of Fig. 2.

Fig. i is a fragmentary rear end elevation of the machine, with parts omitted and Serial: No. 528,077.

others in section to better illustrate the mechanism.

Fig. 5 is an enlarged rear elevation of one of the ring casting carriers for carrying the ring castings to and between the grinding wheels, together with the means used for automatically operating the ring gripping members. i

. Fig. 6 is'a front elevation thereof.

Fig. 7 is a fragmentary vertical section takenon the plane of line 77, of Fig. 5 through one of the ring holding hoppers.

F ig, 8' is a fragmentary vertical section through thegrinding wheels showing a ring casating therebetween being ground at its en s.

Fig. 9 is a fragmentary enlarged horizon tal section taken on the of Fig. 6. V i

Fig. 10 is a fragmentary vertical section taken on the planes of the line 10-l0, of Fig. 5.

Fig. 11 is a transverse'vertical section on line, 11'-11 of Fig. 10.

Fig. 12 is a longitudinal horizontal section through the rear portion of the machine, and showing the pneumatic means for actuating the back grinding wheel fO1'W211"; 1y at periodic intervals.

Fig. 13 is an enlarged vertical transverse section through the aircasing, and showing the. valve mechanism for controlling the flow of the compressed air. used, and

Fig. 14: is a horizontal section taken on the plane of line M ll, of Fig. 13.

Like reference characters. refer to like parts in the different figures of the drawmgs;

In the construction of the grinding machine, an elongated supporting base or bed 1 is provided, on which adjacent its front end, two vertical spaced. apart posts 2 are secured, each at its upper end beingequipped with a. bearing 3. A. shaft 4 is rotatably mounted in said bearings and has a pulley 5 intermediate its ends around which a belt may pass for driving the shaft, and at its rear end has a grinding head or wheel 6 permanently secured.

Two additionalvertical supporting posts 7. and. 8 extend upwardly from and are sup ported by the bed 1, post 7 being at the rear end of the bed and having a hearing at its'upper end, indicated at 9 and post 8 being. farther forward and similarly equipped with a bearing 10.. A shaft 11 is plane of line 99,

lit)

rotatably mounted in the bearings and has a pulley '12 thereon between the two bearings 9 and 10. A second grinding wheel 13 is attached to the front end of the shaft in front of post 8, the front' side of which is spaced a short distance from and parallels the rear vertical face of the first wheel 6. A sleeve 14 is slidably mounted in the bearing 9, its rear end having an enlargement 15, in one side of which a rack 16 is cut. The bearing 9 is formed with an annular 1 shoulder 17 to limit the forward slidable movement of the sleeve 14, which is stopped by engagement of the part against the shoulder. A collar 18 is fixed on the end of shaft 11 and bears against the end of the sleeve 14 at the enlarged portion 15 and the front end of the sleeve bears against the enlargement or hub 20 made at the rear end of the pulley 12, in which hub the usual oil groove 19 is cut. The shaft 11 may rotate at high speed in the sleeve 14 and any longitudinal movement of the sleeve must impart a like longitudinal movement to the shaft 11 whereby the grinding wheel 13 at the front end ofshaft 11 may be moved toward or away from the front grinding wheel 6. But the range of forward movement is limited due to the interposition of the stop made by shoulder 17 in the forward path of movementof the enlargement 15 of the sleeve.

A bracket 21 is attached to or formed integrally with the post 7, lying to one side thereof, and on which lever 22 is pivotally mounted on a vertical stud 23. The inner end of the lever is formed with a sector of gear teeth, as indicated at 24 in mesh with 18 with it so that shaft 11 and its associated grinding wheel 13 may be freed for rearward movement to thereby increase the space between the adjacent faces of the two grinding wheels 6 and 13.

A rod 28 is threaded into the .rear end of shaft 11 and extends a short distance back thereof, hearing at its rear end against a head 29 threaded on to the front end of a short rod 30 which, at its rear end is equipped with a piston 31. The piston is located in a short cylinder 32 carried by the bracket 21 directly behind the rear end of shaft 11, rod 30 passing through the front side of the cylindrical chamber 32. The rear side of the cylinder is closed by a plate 33 formed with a central opening 34, a vertical elongated recess or port way 35 to one side of the central opening, and a lateral port opening 36 extending from its side edge inwardly for a distance toward the opening 34 and then communicating with a circular opening 37 made in the rear side of plate 33 and extending into the plate ed in the member 38, extending through the it rear side thereof, to which at its front end a sector shaped valve 40 is connected, in the front side of which adjacent its lower curved edge an are shaped elongated recess 41 is cut. In one position of the Valve, that shown in Fig. 13, the recess 41 bridges the space between the openings 34 and 37, and it is evident that a free communication is made between the interior of the cylinder 32 and the outside atmosphere, permitting the exhaust of any air in the cylinder. In another position when valve 40 has swung to the right, in Fig. 13, the recess 41 bridges the space between the opening 34 andv the vertical recess 35 so that air from the air chest may enter such recess 41 and pass to the cylinder against the piston 31 to there by move shaft 11 and grinding wheel 13 thereon toward the grinding wheel 6.

A cross supporting beam 42 is located on and at the rear end of the bed 1. Two supporting brackets 48 and 44 are attached to the bed 1 at opposite sides thereof adjacent the post 8 extending outwardly and then upwardly as best shown in Fig. 3. Each adjacent its upper end has a bearing for the front end of a shaft 45. The two shafts extend to the rear paralleling the length of bed 1 and adjacent their rear ends have bearings in the front sides of housings 46, one of which is located at each end of the beam 42 (see Figs. 2 and 4). Within each housing a worm wheel 47 is located, being keyed to the end of the shaft entering the housing and with each worm wheel a worm 48 is in mesh at the upper sides of the wheels. The worms 48 are connected at the ends of a cross shaft 49 on which a pulley 50 is located for the reception of any suitable driving belt for driving shaft 49 from which the two shafts 45 are driven at like speeds but in opposite directions.

At the rear end of one of the shafts 45 a cam wheel 51 is attached having, in the present design of the machine, six cam projections, though it is to be understood that this number may be varied so long as it re mains the same as the number of ring carrying devices on !the ring carrying member at the front ends of shafts 45, later to be described. A roller 52 carried at one end of a lever 53 pivotally mounted between its ends at 54 bears against the cam wheel 51 being normally held thereagainst by any suitable spring or other yielding pressure so that with the rotation of the cam wheel, lever 53 is moved back and forth about its pivot 54. A link rod 55 connects the end of lever 53 with the outer end of a crank arm 56 connected to the rear end of shaft 39. It is obvious, from this construction, that valve is moved back and forth from inlet to exhaust position six times with each revolu tion of the shafts and the grinding wheel 13 is likewise moved forward and back a like number of times.

Brackets 43 and 44 have upwardly extending arms 5'7 and 58, respectively, at tached thereto from the upper ends of which short rods 59 extend forwardly. (in each of these rods downwardly extending arms 60 are adjustably mounted, each at its lower end having an arc shaped member 61 formed integrally therewith. Bear and front sheet metal guide plates 62 and 63 are attached to the members 61, extending from adjacent the edges of the grinding wheels upwardly and outwardly for a distance. The arms 60 associated with the supporting arms 57 are formed with longer are shaped members 61 and longer sheet metal guide plates 62 and 63 are connected therewith extending from the opposite sides of the grinding wheels upwardly and outwardly o in a. direction opposite to the extension of the plates 62 and 63. The plate 62 is longer than plate 63 and has an ejecting spring bar 64 connected thereto, the free end of which is adapted to pass through an opening 65 made in plate 62 beyond the end of the parallel side plate 63. See Fig. 9.

Below the shafts 45 like parallel sheet metal guide plates 66' and 66 are supported in spaced apart relation by brackets 60 adjustably mounted on rods 59 projecting forward from the main supporting brackets 43 and 44. These plates are of arcuate form and at one end come closely adjacent the grinding wheels. The rearmost plate 66' is equipped with a spring ejecting bar like that shown at 64.

The outer ends of the plates 62 and 63*, as well as the outer ends of the like plates 66 come to hoppers 67 of V trough shape in which the continuous ring castings 68 are placed for feeding to the machine. These hoppers are supported on arms 43 and 44 on the brackets 43 and 44. The front plates 63 and 66 extend beyond the open front ends of the hoppers, as shown in Fig. 7, and said ends of the plates are reinforced and supported by rods 69 attached thereto and bent to lie alongside the outer sides of the hop-- pers and attached thereto. The rear ends of the hoppers are closed by ends 70 through which rods 71 slidably pass, each at its front end being equipped with a vertical plate or head 72 to press against the ring castings in the hopper. The rear end of each rod 71 has ahead 71 to which one end of a cable 73 is attached, the same passing over a pulley 75 rotatably mounted at the rear end of the hopper. The rod 71 is thus automatically impelled forward to force the ring castings from the front portion of the hopper.

()n the front end of each shaft 45 a disk 7 6 is permanently secured to which a plurality of radially extending thin sheet metal members 77 are rigidly connected, each in one edge being formed with a substantially semicircular recess 78. In the construction shown there are six of said members secured to each disk, corresponding in number with the cam projections on the cam wheel 51. A second sheet metal member 79 with a like recess in its edge adjacent the member 77 with which it is associated is pivotally mounted on the disk, one for each member 77, its recess 80 together with the recess 78 in the adjacent associated member 77 making a substantially circular opening adapted to receive a ring casting 68. Members 79 are pivotally mounted by attachment thereof to the projecting ends 81 of short shafts 83 rotatably mounted in and passing through the disks 76, the members being placed between enlarged collars 82 on shafts 83 and large washers 84 against which nuts 85v are screwed on to the reduced ends 81 of the shafts.

An arm 86 is mounted on the rear end of each shaft 83, set screws 87 passing through a sleeve 88 formed integral with the end of each arm and bearing against the flattened side of the rear end 83 of each shaft 83, it being obvious that each arm may be adjusted angularly slightly about the axis of its shaft by operation of the screws 87. At the free end of each arm a roller 89 is mounted. Rearwardly extending lugs 90 are formed integral with the disk 76, one for each arm 86 and a short rod 91 is pivotally connected to each arm 86 and passes through an adjacent lug 90, the rod having nuts 92 threaded thereon at its outer end. A spring 93 is located around each rod 91 between the lug 90 and the arm 86 the tendency of which is to move the arm inwardly until nuts 92 engage against lug 90, thus turning the associated shaft 83 to move member 79 attached thereto away from its companion member 77.

A split sleeve 94 is mounted on the front end of the hub of the bearing in brackets 43 and 44 through which shafts 45 pass and is secured thereon by a bolt 95 passing through ears 96 made on the sleeve 94 one each side of the dividing cut therein. This sleeve is formed with a cam projection 97 located in a plane such that the rollers 89 on arms 86 will ride thereover, after first having passed onto the spring bar 98 attached to the sleeve 94 and having a free curved end portion 99 extending toward the cam 97 but with its outer surface located slightly farther out than the outer surface of the cam 97.

With a construction of grinding machine such as described, the operation is as follows: The hoppers at 67 are kept supplied with the rough individual piston ring castings so that there will always be one ready to enter the opening between the members 77 and 7 9 as the same pass in front of the front ends of the hoppers with the rotation of the shafts a5 and attached disks 76 and ring carrying members 77 and 79 attached to the disks. The members 77 and 79 pass between the curved guide plates 62 and 63 and lower guide plates 66 at one side of the machine and the similar plates 66 and 62 and 63 at the other side of the machine. Looking at the side of the machine illustrated in Figs. 5 and 6, as a member 79 passes by the front ring casting 68 in the hopper 67 and its curved recess at 80 comes below the lower edge of the front ring casting. said ring casting is forced forward into the opening between the members 79 and 77, being stopped by the upwardly extending end of the front guide plate 66. The continuation of rotative movement carries the two associated members 77 and 79 downwardly between the guide plates 66 with a ring casting 68 between them. The same operation occurs with each succeeding pair of members 77 and 79. It will be noted that when these ring carrying members come to the hopper and in fact for some time before, the members are separated as far as they will go, the roller 89 on the arm 86 controlling the member 79 not contacting with either the cam 97 or the yielding cam at 99, thereby permitting spring 98 to move the mem- -ber 79 to open position. The ring casting 68, accordingly, freely enters the open space between the members 77 and 79.

After the ring casting has been taken from the hopper it is carried with the two members 77 and 79 downwardly between the guide plates 66 which hold the casting 68 from escape. As the members with the ring casting between approach the grinding wheels 6 and 13 between which they pass, the roller 89 rides upon member 98 and then on to the curved section 99, thereby moving arm 86 and shaft 83 to which it is secured so as to bring member 79 toward its associated member 77 and clasp the ring casting 68 at opposite sides between them. The ring casting is thus firmly held as it starts to pass between the grinding wheels. The grinding wheel 13 is at its rearmost position at this time, the air being exhausted from cylindcr and spring 25 having carriedthe rear grinding wheel backward as previously described. This allows sufiicient space be tween the grinding wheels that no trouble will be experienced in the passage of the rough ring casting between them. As soon as it has entered between the grinding wheels, the cam wheel 51 operates lever 53 for the introduction of compressed air into the cylinder 32 against piston 31, whereby the rear grinding wheel 13 is pressed forwardly. This brings it against the rear end of the ring casting and presses the front end of the casting against the rear side of the front grinding wheel 6. The grinding wheels are driven at high speed and it is evident that the opposite parallel ends of the ring casting are ground off and the outer skin or scale quickly removed. During this time that the grinding is taking place the ring casting is moving upwardly between the grinding wheels and it is held firmly against movement relative to the members 77 and 79 so long as the roller 89 is bearing against the part 99. hen such roller passes from part 99 on to the cam portion 97, the member 79 is slightly'released, thereby freeing the ring casting held by it and its companion member 77 so that the same may spin around in the circular opening made by he recesses 78 and 80. This is very desirable in order to make the planes of the ends of the ring casting absolutely parallel with each other, the spinning or turning of the ring casting accompanied b 1 the rotation of the grinding wheels rough grinding the ends of the ring casting in parallel planes. Passing from the grinding wheels, the member 79 opens still farther as the roller 89 rides off of the cam 97 wholly freeing the ring casting which has been ground so that when it comes to the spring ejector 64 it is thrown forward and out of the opening between the ring carrying members 77 and 79 and away from the machine into any suitable receptacle therefor.

It is apparent that on each side of the machine this operation in its various stages is being continuously carried on. In fact, as shown in Fig. 6, only one' pair of ring carrying members 77 and 79 is empty, the others either carrying rings to the grinding wheels, or away therefrom or taking new rings from the hopper. On the opposite side of the machine, the operation is essentially the same, the only difference being that the rough individual ring castings are carried from the hopper upwardly and over to the grinding wheels between side guide plates 62 and 63, instead of downwardly and under to the grinding wheels and are carried away from the grinding wheels downwardly and outwardly between the side guide plates 66 and ejected under the shaft 45 instead of above it as shown in Fig. 6. This follows from the opposite direction of turning of the shaft 45 and attached parts at the opposite side of the machine. But the grii'iding process is identical and the automatic actuation of the ring carrying and gripping members is the same at both sides of the machine. Evidently, two rings are being ground one at each side of the ma chine simultaneously and two ring castings in the other ring carrying members are always in the same stage" of progress.

The construction is particularly effective for the rough end grinding of the individual ring castings. All that it is necessary for the machine a tendantto do is to keep the hoppers supplied with the ring castings. For different thicknesses of ring castings, it is easy to adjust the various guide plates 62, 63, 66, 62, 63 and 66 to different distances apart, and for different diameters of ring castings, different ring carrying and gripping members 77 and 79 may be mounted on the shafts 83. Adjustment of screw 28 will govern the range of movement of the rear grinding wheel 13. For change in position of the movable members 79 with reference to the fixed members 77, adjusting screws 87 may be operated. The machine is provided with the necessary adjustments that it may be used for the grinding of many difierent thicknesses of ring castings having the same diameter, or for grinding different diameters of ring casting by mere- 1y changing the ring carrying members 77 and '79 to correspond with the size to be ground.

I claim:

1. In combination, a ring carrying hopper for holding a quantity of ring castings, a disk rotatably mounted atone side of the hopper, pairs of ring carrying members mounted on the disk and extending radially therefrom, said ring carrying members being movable across an open end of the hopper and each pair being adapted to receive a ring casting from the hopper as it passes thereby, two rotatably mounted grinding wheels located with adjacent faces parallel between which the ring carrying members pass in their movements, said grinding wheels acting on the ring castings to grind opposite parts thereof, means for driving the grinding wheels, side guide plates between which the ring carrying members pass going to and away from the grinding wheels, and means on one of said plates for automatically ejecting the ring castings from the ring carrying members after grinding thereof.

2. In combination, two rotatably mounted spaced apart grinding wheels, means for driving the same, a disk rotatably mounted at one side of the grinding wheels, pairs of ring carrying members attached to the disk, one member of each pair being rigidly secured to the disk and the other pivotally mounted thereon, said members extending radially from the disk, a hopper having an open end across which the pairs of ring carrying members pass in succession, said hopper being adapted to hold a quantity of ring castings vertically therein, and said pairs of ring carrying members having recesses in adjacent edges for the reception of a ring casting, means for forcing the ring castings in the hopper toward the ring carrying members, means for rotating the disk to carry the ring carrying members between the grinding wheels, and means automatically operated with the rotation of the disk for moving one of the rin carrying members of each pair toward tie other to grip the ring casting between them during a part of the time that the ring casting is between the grinding wheels but freeing the ring casting from said grip before it passes from the grinding wheels, combined with parallel side guide plates between which the ring carrying members pass from the hopper to the grinding wheels, and additional parallel side guide plates between which the ring carrying members pass for a short distance away from the grinding wheels.

3. In combination, two horizontally mounted shafts, grinding wheels on adjacent ends of the shafts having adjacent faces spaced a short distance apart and in para-llelism, means for slidably mounting one of the shafts for longitudinal movement, spring means operatively associated with said shaft tending to move it in a direction to carry the grinding wheel attached thereto away from the other grinding wheel, an air cylinder at the free end of said shaft, a piston therein, means between the piston and shaft whereby movement of the piston in one direction moves the shaft to carry its grind, ing wheel toward the other grinding wheel, valve mechanism for controlling the entrance of compressed air into the cylinder, and means for periodically operating the valve mechanism to periodically admit air to and exhaust it from the air cylinder.

4. In combination, two shafts rotatably mounted in horizontal alinement, grinding wheels on adjacent ends of the shafts having adjacentfac'es parallel and spaced a short distance apart, means for slidably mounting one of said shafts, means for moving said shaft to normally carry the grinding wheel thereon away from the grinding wheel onthe other shaft, pneumatic means associated with the movable shaft for moving it and its attached grinding wheel toward the other grinding wheel, valve mechanism for controlling the pneumatic means, and means for periodically operating the valve mechanism to periodically move the one grinding wheel toward the other.

5. In combination, two rotatably mounted grinding wheels having adjacent faces parallel and spaced a short distance apart, means normally tending to move one of the grinding wheels away from the other, means for continuously driving the grinding wheels, a movably mounted ring carrying mechanism including a plurality of ring casting gripping members adapted to pass between the grinding wheels, a hopper for holding a quantity of ring castings adjacent which the ring carrying mechanism passes to receive ring castings therefrom and carry them to the grinding wheels, and means for automatically operating the gripping members to grip the ring castings and hold the same against movement after first passing between the grinding wheels and thereafter releasing the ring castings for rotative movement before passing from between the grinding wheels, and means for moving said movable grinding wheel toward the other grind ing wheel at the times that ring castings are between them.

6. A construction containing the elements in combination defined in claim 5, combined with parallel spaced apart guide plates between which the ring casting gripping members move toward and away from the grinding wheels, the gripping members receiving but not gripping the ring castings while passing between said plates.

7 In combination two rotatably mounted shafts located in alinement, grinding wheels on adjacent ends of the shafts located with adjacent faces spaced a short distance apart, a support located to one side of the grinding wheels, a shaft rotatably mounted on said support, a disk fixed on the shaft, a plurality of pairs of ring casting gripping members mounted on the disk and extending radially therefrom, said pairs of mem bers having substantially semi-circular recesses cut in adjacent edges and being moved to and between the grinding wheels on rotation of the last mentioned shaft, a hopper for holding a quantity of ring castings and having an open end across which the pairs of ring gripping members pass toreceive ring castings between them, a cam on the support, andnneans interposed between said cam and each pair of gripping members and operable by the cam to move the gripping members of said pairs toward each other to grip the ring casting between each pair at opposite sides at a predetermined position of each pair of ring gripping members, and release the ring casting at a second predetermined position of the gripping members.

8. A construction containing the elements in combination defined in claim 7, combined with yielding means for normally moving one of the grinding wheels away from the other, pneumatic means for forcing said grinding wheel toward the other, means for driving the shaft on which the ring gripping members are mounted, and means controlled by said shaft for rendering the pneumatic means effective at periodic intervals corresponding with the times of entrance of the ring castings between the gripping members between the grinding wheels.

9. In combination, a rotatably mounted shaft, a grinding wheel attached to an end thereof, a sleeve through which the shaft passes and in which it has rotatable bearing, a support for slidably mounting the sleeve, means for connecting the shaft and sleeve whereby on slidable movement of the sleeve the shaft is correspondingly longitudinally moved, a rack formed at one end of the sleeve, a pivotally mounted lever on the support having one end formed into a gear sector engaging the rack, a spring attached to the other end of the lever tending to move the lever and connected sleeve in one direction, and means for periodically moving the shaft and connected sleeve in the opposite direction.

10. In combination, a rotatably mounted shaft, a grinding wheel attached to an end thereof, means for slidably mounting the shaft, spring means associated with the shaft for moving it and its attached grindwheel in one direction, a second rotatably mounted shaft, ring casting carrying members carried by the shaft and movable across the face of the grinding wheel, a cam on the second shaft, an air operated piston associated with the other end of the first shaft for moving it in a direction opposite to that caused by the spring means, valve mechanism for controlling the application to and exhaust of air from the piston, and means for operating said valve mechanism by said cam on the second shaft.

In testimony whereof I affix my signature.

CHARLES E. JOHNSON. 

